High confinement waveguide on an electro-optic substrate

Abstract

The invention relates to an optical device including a passive high confinement waveguide, such as of silicon-rich silicon nitride, on an electro-optic substrate, like lithium niobate, optically coupled to a waveguide in the electro-optic substrate. A wide range of electro-optic devices are enabled by this high confinement waveguide structure, including: directional couplers, compact tap couplers, folded electro-optic devices, electro-optic modulators including ring resonators, electro-optic gratings. Further applications enabled by the present invention include hybrid passive planar lightwave circuits (PLC) integrated with electro-optically active waveguides, using the high confinement waveguide as an intermediary waveguide to transfer optical power between the passive and active components.

1 . A high confinement waveguide comprising:
 an electro-optic substrate having a refractive index n s ;   an optical waveguide within the electro-optic substrate having a refractive index n w  greater than n s ;   a high confinement waveguide on the electro-optic substrate optically coupled to the optical waveguide, the high confinement waveguide having a refractive index n c  greater than n s  such that the electro-optic substrate induces total internal refraction within the high confinement waveguide, and a refractive index n c  greater than n w  such that most of the optical power will couple from the optical waveguide to the high confinement waveguide when the high confinement waveguide is in contact with the optical waveguide.   
   
   
       2 . A high confinement waveguide as defined in  claim 1 , wherein the index change between n s  and n c  is at least 0.02 and as high as 0.2. 
   
   
       3 . A high confinement waveguide as defined in  claim 2 , wherein the index change between n s  and n c  is in the range of 0.02-0.1. 
   
   
       4 . A high confinement waveguide as defined in  claim 2 , wherein the index change between n s  and n c  is 0.05. 
   
   
       5 . A high confinement waveguide as defined in  claim 1 , wherein the electro-optic substrate is lithium niobate and the high confinement waveguide is silicon-rich silicon nitride. 
   
   
       6 . A high confinement waveguide as defined in  claim 1  further including an upper cladding layer encasing the high confinement waveguide on the electro-optic substrate. 
   
   
       7 . A high confinement waveguide as defined in  claim 1 , wherein the high confinement waveguide is terminated by a sharp or blunted taper to force adiabatic transfer of an optical signal into an adjacent waveguide. 
   
   
       8 . A high confinement waveguide as defined in  claim 7 , wherein the sharp or blunted taper of the high confinement waveguide overlaps a tapered end of the optical waveguide to force adiabatic transfer of an optical signal between the high confinement waveguide and the optical waveguide in either direction. 
   
   
       9 . A high confinement waveguide as defined in  claim 1 , wherein, the high confinement waveguide includes an abrupt bend having beveled corner comprising a vertical sidewall for reflecting an optical signal around the abrupt bend. 
   
   
       10 . A high confinement waveguide as defined in  claim 1 , wherein the high confinement waveguide is at least partially disposed in a trench in the surface of the electro-optic substrate. 
   
   
       11 . A high confinement waveguide as defined in  claim 10 , wherein the high confinement waveguide is partially disposed in a trench having a taper for providing a gradual transition from lower to higher confinement of the optical signal. 
   
   
       12 . A high confinement waveguide as defined in  claim 1 , wherein the high confinement waveguide and the optical waveguide are coincident to form a hybrid waveguide for single mode transmission. 
   
   
       13 . A high confinement waveguide as defined in  claim 12 , wherein the electro-optic substrate has a surface profile defining a ridge, and the optical waveguide is formed in the ridge with the high confinement waveguide coincident above the optical waveguide on the ridge. 
   
   
       14 . A high confinement waveguide as defined in  claim 12 , wherein the optical waveguide comprises diffused titanium and the high confinement waveguide comprises silicon-rich silicon nitride. 
   
   
       15 . An electro-optic device comprising:
 an electro-optic substrate having a refractive index n s ;   at least one optical waveguide within the electro-optic substrate for transmitting an optical signal through the device for electrically-induced modulation;   at least one high confinement waveguide having a refractive index n c  greater than n s  optically coupled to the at least one optical waveguide through at least one taper for adiabatic transfer of the optical signal.   
   
   
       16 . An electro-optic device as defined in  claim 15 , wherein the device comprises a directional coupler having a first waveguide and a second waveguide disposed for evanescent coupling between them, and at least one of the first and second waveguides is a high confinement waveguide. 
   
   
       17 . An electro-optic device as defined in  claim 16 , wherein the first and second waveguides are high confinement waveguides vertically separated by a buffer layer between them. 
   
   
       18 . An electro-optic device as defined in  claim 17 , wherein the first high confinement waveguide is a hybrid waveguide coincident with an optical waveguide in the electro-optic substrate. 
   
   
       19 . An electro-optic device as defined in  claim 16 , wherein the first and second waveguides each comprise a hybrid waveguide having a high confinement waveguide coincident with an optical waveguide in the electro-optic substrate, and the first and second waveguides are disposed in a horizontally separated side-by-side configuration. 
   
   
       20 . An electro-optic device as defined in  claim 19 , wherein the optical waveguides of the first and second hybrid waveguides overlap in a coupling region. 
   
   
       21 . An electro-optic device as defined in  claim 16 , wherein the directional coupler comprises a tap coupler and the first waveguide is an optical waveguide and the second waveguide is a high confinement waveguide having a small bend radius. 
   
   
       22 . An electro-optic device as defined in  claim 15 , wherein the device comprises a Mach-Zehnder interferometer comprising an input optical waveguide, a first optical splitter, a first arm and a second arm, an optical combiner and an output optical waveguide, and wherein the first arm and second arm of the Mach-Zehnder interferometer comprise optical waveguides including a plurality of small radius bends comprising high confinement waveguides optically coupled with adiabatic tapers to the optical waveguides, in order to reduce a length of the electro-optic device. 
   
   
       23 . An optical device as defined in  claim 15 , wherein the device comprises a ring resonator including a straight waveguide having a high confinement waveguide coincident with an optical waveguide in the electro-optic substrate, and a ring waveguide comprising a high confinement waveguide coincident with an optical waveguide in the electro-optic substrate disposed for evanescent coupling between them. 
   
   
       24 . An electro-optic device as defined in  claim 15 , wherein the device comprises a Mach-Zehnder interferometer comprising an input optical waveguide, a first optical splitter, a first arm and a second arm, an optical combiner and an output optical waveguide, and wherein the first arm and second arm of the Mach-Zehnder interferometer comprise optical waveguides including at least one ring resonator optically coupled to the first arm, and at least one ring resonator of equal number optically coupled to the second arm, and wherein the at least one ring resonator coupled to each arm comprises a high confinement waveguide disposed such that the at least one ring resonator coupled to the first arm and the at least one ring resonator coupled to the second arm have equal bias voltage and opposite signs. 
   
   
       25 . An electro-optic device as defined in  claim 23 , wherein the ring resonators comprise hybrid waveguides of high confinement waveguides coincident with optical waveguides in the electro-optic substrate. 
   
   
       26 . An electro-optic device as defined in  claim 23 , wherein the ring resonators comprise optical waveguides including a plurality of small radius bends comprising high confinement waveguides optically coupled with adiabatic tapers to the optical waveguides. 
   
   
       27 . An electro-optic device as defined in  claim 15 , wherein the device comprises a grating formed as a periodic structure along the length of the high confinement waveguide optically coupled to the optical waveguide in the electro-optic substrate. 
   
   
       28 . An integrated optical device comprising:
 an electro-optic element disposed on an electro-optic substrate having a refractive index n s ;   a passive optical element; and   an optical waveguide circuit through the electro-optic element and the passive optical element, wherein the optical waveguide circuit includes a high confinement waveguide on the electro-optic element having a refractive index n c  higher than n s  and a high confinement waveguide on the passive optical element having a refractive index n p  optically coupled to the high confinement waveguide of the electro-optic element.   
   
   
       29 . An integrated optical device as defined in  claim 28 , wherein the high confinement waveguide of the electro-optic element is optically coupled to the high confinement waveguide of the passive optical element through adiabatic tapers. 
   
   
       30 . An integrated optical device as defined in  claim 28 , wherein the high confinement waveguide of the electro-optic element is optically coupled to the high confinement waveguide of the passive optical element through a directional coupler between the high confinement waveguides. 
   
   
       31 . An integrated optical device as defined in  claim 28 , wherein the electro-optic element comprises a lithium niobate waveguide device, and wherein the passive optical element comprises a silica-on-silicon waveguide device. 
   
   
       32 . An integrated optical device as defined in  claim 28 , wherein the electro-optic element and the passive optical element are optically coupled as a flip-chip assembly, where the high confinement waveguides are formed on a top surface of the electro-optic element and on a top surface of the passive optical element, and one of the electro-optic element and the passive optical element is inverted to physically contact the high confinement waveguides together. 
   
   
       33 . An integrated optical device as defined in  claim 32  further including an index matching optical glue disposed between the high confinement waveguide of the electro-optic element and the high confinement waveguide of the passive optical element.